//懒汉模式————实现单例模式
class SingletonLazy{
    volatile private static SingletonLazy instance = null;
    public static SingletonLazy getInstance(){
        // 这个条件, 判定是否要加锁. 如果对象已经有了, 就不必加锁了, 此时本身就是线程安全的.
        if(instance == null){
            synchronized (SingletonLazy.class){
                if(instance == null){
                    instance = new SingletonLazy();
                }
            }
        }
        return instance;
    }
    private SingletonLazy(){}
}
public class ThreadDemo3 {
    public static void main(String[] args) {
        SingletonLazy s1 = SingletonLazy.getInstance();
        SingletonLazy s2 = SingletonLazy.getInstance();
        System.out.println(s1 == s2);
    }


}
